This invention is directed to telephone systems and, more particularly, to tone-to-pulse converters suitable for converting the DTMF (Dual Tone Multi Frequency) signals generated by push-button-type telephones into rotary dial-type pulses.
Tone-to-pulse converters for converting DTMF signals of the type generated by push-button telephones into rotary dial-type pulses are well known and widely used. These devices are required in telephone systems that include switching systems that are only operable by rotary dial-type pulses, not by DTMF signals.
Tone-to-pulse converters of this nature fall into two general categories. In one category are allotter systems wherein a plurality of tone-to-pulse converters are assigned in an allotted manner to a plurality of tip and ring telephone lines on an as-needed basis. In the second category are dedicated tone-to-pulse converters. In a dedicated system, a tone-to-pulse converter is "hard wired" to a single set of tip and ring leads. An example of a dedicated tone-to-pulse converter is the model M-161 tone-to-pulse converter produced by the Tel-Tone Corporation, Kirkland, Wash. the assignee of the present application. The present invention is particularly suitable for use with a dedicated tone-to-pulse converter.
Tone-to-pulse conversion systems, in general, regardless of whether or not they are of the allotter variety or of the dedicated variety are adapted to receive DTMF signals of the type generated by push-button telephones. The signals are stored and used to create sequential series of rotary dial-type pulses, each series equal in number to the number of a related push-button. More specifically, when a push-button is depressed, it causes a unique combination of high and low frequency tones (one of each type) to be generated. A tone-to-pulse converter receives these tones and tests them to determine whether or not one-and-only-one high frequency tone and one-and-only-one low frequency tone exists. Assuming this test, and other tone time tests are passed, a related binary signal is stored and used to create a series of rotary dial-type pulses that are applied to the output tip and ring leads, after the telephone line has been split. These pulses are recognized by downstream switching systems and utilized to create the desired telephone interconnection.
In many tone-to-pulse conversion systems, a time-out circuit is included. The time-out circuit specifies the maximum time period that can occur: (1) between the time the subscriber goes OFF HOOK and depresses the first button; and, (2) between button depressions (interdigit time periods). If the maximum time period elapses before these actions take place, the system is automatically reset and the subscriber must go ON HOOK and OFF HOOK before he can successfully dial. While the time-out circuit is usually included to disable the tone-to-pulse converter subsequent to an entire series of digits being "dialed," it is normally enabled when the subscriber initially goes OFF HOOK. Thus, in the past, if the subscriber did not dial the first digit within the time-out circuit's time period, the tone-to-pulse converter was automatically disabled from the circuit and he could not thereafter dial effectively without first going ON HOOK and then OFF HOOK. This disablement has created a problem in the past because while the converter was disabled, the dial tone was still being heard by the subscriber. More specifically, many telephone switching systems, such as step-by-step switching systems, do not include a time-out circuit that disables the dial tone some predetermined period after a telephone goes OFF HOOK, if a subscriber does not dial. In other words these systems generate a dial tone as long as a telephone is OFF HOOK, until a first digit is dialed. Thus, the subscriber is not informed by a lack of dial tone that the converter is disabled and he can no longer "dial" a desired telephone number. This invention is primarily directed to eliminating this problem of prior art tone-to-pulse conversion systems, particularly those of a dedicated nature.
Therefore, it is an object of this invention to provide an apparatus for preventing the time-out portion of a tone-to-pulse conversion system from operating until a first DTMF digit is dialed.
It is another object of this invention to provide an inexpensive electronic circuit that prevents a dedicated tone-to-pulse converter from automatically being inhibited by the automatic operation of a time-out circuit until after a first DTMF signal has been received by the tone-to-pulse converter.
It is a still further object of this invention to provide a tone-to-pulse converter with stop time-out until after first DTMF digit dialed circuit that prevents the tone-to-pulse converter from being disabled until a first DTMF signal has been received and used to initiate the out pulsing of a related series of rotary dial-type pulses.